A primary feature of a helicopter is its ability to execute a landing at nearly any location, and does not necessarily require a dedicated runway as with many other types of aircrafts. A typical aircraft landing involves the pilot receiving necessary landing information from operators located at a nearby aircraft control station and/or at an airport at which the landing will take place. If the pilot is landing the aircraft at a remote location where the necessary landing information cannot be acquired from an external source, then the information must be obtained by other means. A crucial component of this information is various parameters relating to the wind conditions at the desired landing point, such as the wind speed and the wind direction. The wind parameters must be known with a sufficiently high degree of accuracy. There may be a significant difference between the local wind conditions at the landing point from those in nearby regions, even when comparing between relatively short distances. Therefore a global value of the wind parameters in the general vicinity of the landing aircraft may not be sufficiently accurate for the landing requirements. Furthermore, the wind parameters are variable and may change abruptly. Various entities or items may suddenly shift to a location along the wind path, which may change or influence the wind parameters. In some situations, the pilot is not aware of the exact landing point well in advance of the actual landing, and may be forced to determine the precise location, or to alter a previously selected landing point, according to various constraints and changing conditions. In addition, the landing point may be at a remote location where there is limited or no access to landing assistance individuals and/or which lacks nearby aircraft control stations (e.g., due to topographical factors, such as a lake, a mountain, or other types of difficult to reach terrain). Such constraints further serve to complicate the ability to accurate the wind parameters and other necessary landing information within a sufficient time period and a sufficient degree of accuracy.
One approach for real-time landing zone signaling, commonly employed by military and paramilitary forces, involves the use of smoke grenades. The emanating smoke can provide the pilot with an indication of the wind direction at the landing point. While smoke grenades are simple to deploy and may be used simultaneously for additional purposes, they are also potentially dangerous due to the contained chemicals and are thus typically restricted to authorized personnel. In addition, a smoke grenade cannot be deployed over water, and once the smoke from a first grenade has fully evaporated, a new grenade must be used. Another approach is to install a portable windsock or other highly visible wind measurement instrument at the landing point in real-time by people on the ground. However, such a windsock is relatively large and requires time to assemble, and thus entails informing the necessary individuals at the actual landing point sufficiently ahead of time.
There are various types of measurement instruments and techniques known in the art for measuring wind speed and wind direction. A wind vane, also known as a “weather vane” or a “weathercock”, is generally embodied by an asymmetrically shaped pointer mounted at its center of gravity onto a vertically oriented rod, such that one end of the pointer is oriented along the direction of the wind. The wind vane may also include a compass, such as a four-arm cross denoting the reference directions (North, West, East, South), providing reference axes for the pointer alignment. A related type of instrument is a propeller or windmill anemometer, which has a number of flat or helicoidal vanes rotating along an axis parallel to the direction of the wind. The wind speed can be calculated a function of the angular rotation of the vanes.
A windsock, also known as a “wind sleeve” or “wind cone”, is a conical hollow tube made of fabric, which is mounted on a freewheeling pivot such that the tube points away from the direction of the wind blowing through it. Windsocks are typically brightly colored to enhance visibility, and are commonly employed at airports (to assist pilots), at chemical plants (due to risks of gas leakages), and along highways (for vehicle drivers).
A pitot tube is a pressure measurement instrument, consisting of a tube positioned parallel to the direction of a fluid stream and attached to a manometer (pressure gauge), providing a measurement of the fluid flow velocity. A tube anemometer is generally embodied by a U-shaped tube containing a liquid manometer where one end of the tube is bent horizontally facing the wind while the other end remains vertical parallel to the wind flow. The wind blowing into the horizontal tube end increase the pressure on one side of the manometer, while the wind flowing along the vertical tube end barely effects the pressure at the other side, such that the resulting liquid change in the tube provides an indication of the wind speed. Another type of anemometer that operates by measuring wind pressure is a plate anemometer, which is simply a vertically suspended flat plate, where the wind pressure against the plate surface is balanced by a spring. The spring compression determines the force applied by the wind against the plate. Plate anemometers provide poor response to light winds and variable wind conditions, and inaccuracies with strong winds.
A sonic anemometer utilizes ultrasound waves to measure wind speed, based on the propagation time of the ultrasound waves between a pair of transducers. Multiple ultrasonic transducers may be combined to produce a three-dimensional model of the wind flow. Sonic anemometers are well-suited for turbulence measurements due to their high temporal resolution, and are also relatively robust and durable due to a lack of moving parts. However, sonic anemometers are susceptible to inaccuracies during precipitation (e.g., rainy weather), and also may require compensation for the effects of the supporting structure.
A laser Doppler anemometer operates by measuring the reflected backscatter of a transmitted laser beam and the associated Doppler shift. The measured Doppler shift is used to calculate the speed of the particles in the air causing the backscattering, which corresponds to the wind speed in the surrounding area.
A ping-pong ball anemometer involves a simple configuration of a ping-pong ball (or similar lightweight object) suspended from a string. A measure of the angular displacement of the ping-pong ball provides an indication of the wind speed, while the displacement direction corresponds to the wind direction.
U.S. Pat. No. 4,080,925 to Moore, entitled “Portable surface wind indicator”, is directed to a portable wind indicator that can be dropped from an aircraft in remote locations. The wind indicator includes a central body member, and a plurality of elongated arms extending outwardly from the central member. Wind indicating means, such as a ribbon or flag, is attached to the outer end of each arm. The arms are spaced and arranged such that when the indicator is dropped from an aircraft, it will land supported by three arms with another arm extending upward into the air for indicating the wind direction.
U.S. Pat. No. 5,179,907 to Galbraith, entitled “Flag and buoy apparatus”, is directed to a flotation apparatus to support a flag which may be placed in the water to indicate the presence of a scuba diver. The apparatus includes a body with a plurality of recessed receptacles, a plurality of buoyant arms, a flag, and a pole assembly. Each arm is received in a receptacle and extends radially from the body, while also being tethered to the body. The pole assembly extends axially from the body to support the flag. The arms and the pole assembly may be detached from the body for storage of the apparatus.
U.S. Pat. No. 6,378,820 to Mooney et al, entitled “Apparatus and method for mounting banners”, is directed to a mounting apparatus for a banner or outdoor structure, susceptible to tearing by strong wind loads. The apparatus includes an arm and a base. The arm includes a proximal portion, a distal portion for holding a banner, and a spring portion connecting the proximal portion to the distal portion. The base includes a plate, a receiver and straps, and is adapted for attaching the proximal portion of the arm to a pole.
U.S. Pat. No. 6,748,896 to Hunsley, entitled “Streamer flag attachment”, is directed to an attachment for providing a visually appealing enhancement to a flag pole. The attachment includes a circular loop that includes an elastic material formed into a closed ring defining a central opening. The attachment further includes a sleeve-like streamer holder attached to the loop, and a plurality of elongated strips of flexible material attached to and extending radially from a portion of the streamer holder. A user can securely mount the attachment by coupling the circular loop around the flag pole and allowing the loop to grip the flag pole surface, thus holding the attachment in place
U.S. Pat. No. 7,574,973 to Markham, entitled “Emergency rescue device and method”, is directed to a device including an integrated emergency rescue line and reflective locator for visually locating the area of a person to be rescued. The device includes a canister that houses a plurality of reflective strands or ribbons. A strap secures the rescue device to a user. When the device is activated, the strands are ejected away from the user in a multi-directional pattern. A rescuer may then pull on one of the exposed strands to exactly locate the victim. The activation element may include a combustible propellant, an explosive charge, or compressed source of gas integrated within the canister.
U.S. Patent Application Publication No. 2003/0126774 to Lim et al, entitled “Wind indicator”, is directed to a wind indicator. The indicator includes a body with a frame including a spindle axis and a web. A pivot connected to the frame permits the body to rotate about a pivot axis. A spindle disposed on the spindle axis is rotatable about the spindle axis. The spindle includes first and second hubs, each of which include a central body portion and at least one vane support receiving element. At least one element connects the first hub to the second hub to maintain the two hubs in positional relation with respect to one another. At least one vane extends between the vane support receiving elements on the two hubs. The vane captures air movement and translates it into rotational movement of the spindle.